Generic fantasy setting. Necrophilia. Corruption. Eventual snuff.

A young lad from a humble village stumbles upon the body of a decapitated female warrior. From the damage to the surrounding trees it's clear she has lost a fierce battle. The head is nowhere in sight. (If I described the body here it would never end - so just think amazon from Dragon's Crown.) The male protagonist loses his virginity with the body. There's no sense of degeneracy or evil in his actions, but it does condemn him to take a different path through life. After his time with his newfound lover is cut short by decomposition, he resolves to never let it happen again. He throws himself into research and learns everything he can about death, motivated by love (or perhaps lust that he mistakes for love) he unknowingly descends into necromancy.

The story could go in all sorts of directions from here, from what I envisage it would definitely involve hunting female heroes. Though likely it starts "innocently" with him simply sending a young adventurer on a quest he knows she can't win.